Sound processors produce sound by controlling digital data, which is transformed into a voltage by means of a digital-to-analog converter (DAC). This voltage is used to drive a speaker system to create sound. Sound processors, which are wave-table-based, use sound data from memory as a source, and modify that sound by altering the pitch, controlling the volume over time, transforming the sound through the use of filters, and employing other effects. These modifications to the source sound are controlled through a set of parameters.
Polyphonic sound processors create multiple sounds simultaneously by creating independent sound streams and adding them together. Each separate sound that can be played simultaneously is referred to as a voice, and each voice will have its own set of control parameters. The set of control parameters to control a voice is referred to as a parameter block.
FIG. 1 is a block diagram of a conventional system 50 for controlling sound data. The system 50 includes a host processor 52, a sound processor 54, and a memory unit 56. The memory unit 56 stores sound data 60 and parameter blocks, which contain control parameters for the sound data. For an advanced sound processor, there are many control parameters that the host processor 52 is able to write in order to control the production of sound by the sound processor 54. There can be several hundred control parameters per voice. Because of the large number, it becomes preferable to have them reside in the main system memory instead of in registers or random access memory (RAM) in the sound processor.
Also, with a large number of control parameters, it becomes important for both the host processor 52 and the sound processor 54 to access the control parameter blocks 62 without conflict. It may require many cycles for the host processor 52 to update the control parameters, and it may require many cycles for the sound processor to read all of the control parameters. Since many of the control parameters are related, if no method were used to avoid conflict, the sound processor 52 may read an inconsistent set of control parameters for a voice.
One conventional solution, which avoids conflict by the host processor 52 and the sound processor 54 in accessing parameter blocks, is to use locking mechanisms 64. Typically, there is a locking mechanism for each parameter block. If the host processor 52 or the sound processor 54 wants to access a particular parameter block, the host processor 52 or sound processor 54 will test a lock bit. If the lock bit was not set, the host processor 52 or sound processor 54 will set the lock bit and know that it can access the parameter block. If the lock bit was set, then the parameter block is currently being accessed, and the host processor 52 or sound processor 54 must wait until the parameter block is not locked before accessing it. The disadvantage of this solution is that each processor must wait for the parameter block to be free before accessing it. This may result in wasted time and reduced performance.
Another problem with this solution is that when locking a parameter block in system memory, a “test and set” instruction is necessary. This instruction is necessary because two modules may test whether the block is locked before either has a chance to set the lock bit. In this case, an error condition can occur where both modules think that they can access the memory block.
Accordingly, what is needed is a more efficient system and method for controlling access to parameter blocks of a sound processor. The system and method should be able to simple, cost effective and capable of being easily adapted to existing technology. The present invention addresses such a need.